From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock Date: Mon, 07 Feb 2011 18:26:43 +0200 Message-ID: <4D501D43.5060608@redhat.com> References: <4D4BCB97.6000900@siemens.com> <4D4C698A.4010201@redhat.com> <4D4FD8EE.6040009@siemens.com> <4D4FFD97.6010805@redhat.com> <4D5008F0.5060200@siemens.com> <4D500C9F.2080501@redhat.com> <4D50120F.4030809@siemens.com> <4D501547.6040907@redhat.com> <4D501698.1000507@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Zachary Amsden , Marcelo Tosatti , kvm , Linux Kernel Mailing List To: Jan Kiszka Return-path: In-Reply-To: <4D501698.1000507@siemens.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 02/07/2011 05:58 PM, Jan Kiszka wrote: > On 2011-02-07 16:52, Avi Kivity wrote: > > On 02/07/2011 05:38 PM, Jan Kiszka wrote: > >>> > >>> I don't know as it is allowed to sleep, it doesn't call any sleeping > >>> functions to my knowledge. What worries me in the RT case is that the > >>> spinlock acquired for hardware_enable might be preempted and run on > >>> another CPU, which obviously isn't what you want. > >> > >> I see now, there are calls to raw_smp_processor_id. > >> > >> I think it's best to make this a raw lock. At this chance, some > >> read-only users of vm_list should be rcu'ified. Will have a look. > > > > vm_list is rarely used, for either read or write. I don't see the need > > to rcu it. > > Avoid that code under this lock expands the preempt-disabled period, > specifically under -rt, and specifically as the number of objects over > which we loop is user-defined. Good point; even under non-rt. (well, actually, cpufreq_notifier and kvm_arch_hardware_enable are already non preemptible, and the stats code should just go away?) -- error compiling committee.c: too many arguments to function